1. Field of the Invention
The field of the invention is directed to the provision of a simple yet highly effective method of and means for providing A.C. motors with an infinitely adjustably output torque within the limits of zero to full nameplate rating.
2. Description of the Prior Art
Applicant is aware of the following patents which, in his opinion, are most relevant to the subject invention.
U.S. Pat. No. 2,748,334 to G. L. Miller dated May 29, 1956 discloses two variants of a VARIABLE SPEED INDUCTION MOTOR wherein means are provided for imparting endwise axial movement to the stator 26 relative to the outer periphery of rotor 12 for selectively varying the amount of magnetically responsive flux introduced into the magnetic field at any time by the stator. The rotor is provided with a first portion 18 and a second portion 20 wherein the portion of the circumference of portion 22 is cut away at 26 to provide an annular groove or gap which completely encircles the periphery of portion 22. This reference in FIGS. 4-7 also illustrates means whereby the rotor, per se, is mounted for endwise axial movement relative to the stator which is fixedly mounted relative to the inner surfaces of the motor housing.
The change in the axial relationship of the axially shiftable stator relative to the axially fixed rotor, or the change in the axial relationship of the axially displacable rotor relative to the axially fixed stator is utilized to alter the path for the stator flux in such a manner as to achieve a change in output speed of the rotor. The invention of the subject application is distinguishable from the disclosure of this reference since in applicant's device both the rotor and the stator are at all times fixed against a relative axial movement, and control of the flux is accomplished by advancing or retracting magnetic control rods axially into and out of control-rod-receptive channels provided through the stator.
U.S. Pat. No. 2,959,694 dated Nov. 8, 1960 discloses an ADJUSTABLE SPEED SQUIRREL CAGE INDUCTION MOTOR of the type which includes a stator which is axially shiftable relative to and along the length of the rotor for thereby altering the path of the stator flux to the rotor to control the rotational speed of the rotor wherein the rotor includes a low resistance induction section 19 which is disposed adjacent and in axial alignment with a high resistance induction section 20. The stator element 22 is provided with conventional polyphase windings 23 said stator being longitudinally slideable internally of the motor frame relative to the outer periphery of the rotor.
The operation of U.S. Pat. No. 2,959,694 is described in column 4, lines 24-50 as follows:
"In operation, at start, with the stator 22 over only the nondriving, noninductive rotor section 21, the latter provides a magnetic body of low reluctance acting as a shunting element for the stator field to maintain a high counter electromotive force in the stator winding and avoid undue current drain on the line. To start rotation of the rotor at low speed, the reversible control motor 33 is operated to move the stator from right to left (FIG. 1), gradually bringing the stator over the high resistance rotor section 20 to give the motor high starting torque with high slip and low current drain from the line. Then further operation of the control motor 33 to move the stator on over the low resistance section 19, further reduces the effective resistance of the combined driving rotor sections 19 and 20 gradually bringing the motor to a characteristic giving low slip and substantially constant speed with load changes."
"To reduce speed or bring the motor to a stop, the control motor 33 is reversed; moving the stator back toward the nondriving, rotor section until the desired reduction in motor speed is obtained, or all the way to the nondriving section if stoppage is desired. Intermediate positions of the stator will give intermediate speeds which may be maintained for a considerable time without undue heating due to the effective cooling system for dissipating heat generated in the windings, particularly the high resistance winding."
U.S. Pat. No. 4,025,840 to G. E. Brissey et al dated May 24, 1977 discloses a PERMANENT MAGNET GENERATOR WITH OUTPUT POWER ADJUSTMENTS BY MEANS OF MAGNETIC SHIMS which are designated by the numeral 11 and which, as clearly illustrated in FIGS. 1 and 3, are disposed in fixed, overlying relationship with the outer surface of nonmagnetic insulated wedges 24 which in turn overlie the upper portions of the slot liners 23 which encapsule coils 20, 21, and 22 wound around the pole stems located in compartments which are disposed in slots 12 between adjacent teeth 13 which extend radially from yoke 14 of the stator. The stator teeth 13 are of the salient or overhanging type and include a pair of oppositely extending salient tip portions 15. Magnetic shims 11 are inserted endwise into one or more of a plurality of the stator slots 12 being wedged beneath overhanging portions 15 of the stator teeth and the upper surface of the insulating wedge 24 after which the triangular ends 26 of the magnetic shims (not FIG. 2) are turned upward for engaging the opposite ends of tip portions 15 of a stator tooth 13 to thereby effectively prevent the endwise removal of a shim until and unless an upturned end 26 thereof has been bent downwardly back to the plane of the shim, per se, after which it may be slid endwise from between adjacent teeth 13.
This reference teaches that by the judicious selection and placing of shims in certain specific selected slots of the stator, the flux leakage between the stator and rotor at the location of the shims may be increased whereby the leakage inductance of the windings in those slots in which the shims have been placed will, under increased load, reduce the output from the selected windings without in any way effecting the output from the other windings of those particular slots which have not been provided with a magnetic shim strip 11.
U.S. Pat. No. 2,342,720 dated Feb. 29, 1944 to J. H. Blankenbuehler discloses a WELDING GENERATOR wherein the reluctance of the path of the magnetic leakage flux between the arcuate shoe member 19 and 20 and the field pole members 11 and 12 are selectively varied by means of a movable magnetic shunt member 34 which is positioned in bridged relation between the adjacent portions of the shoe members 19 and 20 and wherein the movable shunt member 34 is suitably mounted for endwise axial movement relative to said pole members, thereby changing the output welding current as delivered by the generator.
Abstract #209,189 published Apr. 21, 1953, of H. K. Ziegler discloses an ALTERNATING CURRENT MACHINE which has a stationary armature 33 with a winding thereon, a rotor 21 for producing a permanent magnetic field, and a housing 30. A laminated soft iron ring-shaped magnetic shunt member is supported coaxially of the rotor shaft 28 and is adjustably attached to the housing 30 and/or the rotor shaft 28. The ring-shaped magnetic shunt is adjustable axially of the rotor shaft by means of a suitable mechanism in order to vary the amount of flux from the permanent magnet rotor which links both the rotor and the armature winding. If desired a damper winding 27 may also be provided.
U.S. Pat. No. 978,638 to C. A. Parsons et al dated Dec. 13, 1910 relates to REGULATION OF DYNAMO ELECTRIC MACHINERY wherein the A.C. output voltage of a polyphase A.C. generator is regulated by providing a secondary winding for the leakage path of the flux.
U.S. Pat. No. 1,231,588 to L. T. Frederick et al dated July 3, 1977 discloses MAGNETIC MATERIAL from which magnetic shims are produced for reducing the eddy current loss in a stator or rotor by narrowing the air gap in the stator or rotor slot openings. The composite shim material is composed of both nonmagnetic and magnetic material.
Applicant is also aware of the disclosure of German Pat. No. 817,008 310/190--German Pat. No. 233,235 310/190--and German Pat. No. 159,241 310/190, and he is also aware of U.S. Pat. No. 3,226,582 to S. Beckwith dated Dec. 28, 1965 which discloses ADJUSTABLE TORQUE INDUCTION MOTORS and U.S. Pat. No. 3,042,820 dated July 3, 1962 to A. Diamond which discloses a SERVO MOTOR WITH ADJUSTABLE VELOCITY DAMP. However, it is considered that none of the last 5 mentioned references are as relevant as any of the first seven mentioned references, the disclosures of which have been more fully discussed hereinabove.
The disclosure of none of the 12 aforementioned references when considered singly or in combination neither teach nor disclose the inventive concept for accomplishing the concept of torque control of an alternating motor as disclosed in this application, nor is the invention of this application obvious, as that term is used in U.S. C. Title 35, Section 103.